MODAL IDENTIFICATION OF CABLE-STAYED PEDESTRIAN BRIDGE

The vibrations of a cable-stayed pedestrian bridge are measured and co mpared with a numerical model, and used to produce improved estimates of the structural properties. Fourteen deck modes with frequencies und er 16 Hz were identified using the impact hammer technique. The dampin g of all but one of the modes was measured at 0.75%, in spite of a woo d deck. The numerical model consisted of a three-dimensional finite el ement analysis which incorporated nonlinear cable effects. The experim ental and numerical results were shown to be highly correlated by visu al inspection, the MAC, and the CoMAC. The primary differences were: ( 1) Two of the experimental mode shapes showed a slight asymmetry that was not present in the numerical modes; and (2) the measured natural f requencies were consistently higher than the numerical frequencies. Pa rameter estimation using eigenvalue sensitivities with changes of less than 12% in the nominal values helps reconcile the experimental and n umerical differences.